1. Field of the Invention
The present invention relates generally to dryers, and more particularly, relates to a round cylindrical industrial dryer employing a controlled environment system for the recovery of flammable solvents. A traveling web of material is floated by opposing air bars.
2. Background of the Invention
It is known in the prior art that processes which involve flammable vapors must often be accomplished in sealed chambers. It is also particularly important to protect operators and other workers in the area from dangers associated with inhaling certain solvents. In the past, most of these chambers have been rectangular in shape. Though this shape is convenient for some purposes, fabrication tends to be difficult and expensive. Rectangular structures are more prone to weld or stress cracks.
U.S. Pat. No. 4,826,707 issued to Schwarz et al. on May 2, 1989, shows such a sealed chamber in a cylindrical shape. The process taught by Schwarz et al. is the coating of a web of material while cooling the material to avoid structural damage. The environment of the chamber of Schwarz et al. is easily controlled because the entire web of material undergoing processing is contained within the sealed chamber.
At times, however, it is desirable to process a continuous web of material of considerably greater volume than can be practically contained within the sealed chamber. Therefore, a continuous web of material must travel through the chamber making it difficult to control the atmosphere within the chamber. The most common technique is through the use of an inert gas to backfill the chamber at a pressure which is slightly greater than atmospheric pressure. This permits the maximum control of the environment within the chamber.
The interior of the cylinder of Schwarz et al. consists of a single processing chamber. This is disadvantageous when the process to be accomplished is a drying operation because it restricts the process to an atmosphere of single temperature, pressure, and composition. Use of a number of chambers as taught by Schwarz et al. is possible, but tends to be expensive and is much more likely to leak.
When the process involves the release of a flammable vapor, such as the removal of a flammable solvent vapor, great care must be exercised in maintaining a low oxygen level within the sealed chamber. A common prior art technique is to purge the entire chamber when the oxygen level exceeds a predetermined threshold level. This often results in unacceptable down time of the process and unacceptable waste of the inert gas used to backfill the chamber. Such purging may itself present a safety risk because the contents of the chamber often cannot simply be vented to the air.
The present invention overcomes the disadvantages of the prior art by providing a zoned cylindrical dryer for removing solvents from a traveling web floated by a plurality of air flotation bars or like support structure.